Gold, one of the most commonly studied plasmonic nanomaterials, has a high thermal conversion efficiency. However, its high cost, low thermal durability, and complicated synthesis procedures prevent its application on a large scale. To address these issues, cost-effective, inert metal nitrides such as titanium nitride (TiN) can be considered as alternative materials. TiN has high thermal stability and exhibits metallic properties at visible wavelengths. In this study, TiN nanoparticles (NPs) were prepared using a facile ball milling method suitable for large-scale production. The time and rotational speed of the ball mill were varied to evaluate the effect of particle size and the amorphous content of TiN NPs on the photothermal properties under white light. Moreover, the effects of particle size and the amorphous content on photoheating were evaluated by measuring the increase in temperature of a dispersive TiN NP solution exposed to a white light-emitting diode (LED) source. We found that TiN NPs with a diameter of approximately 100 nm exhibited a maximum temperature increase of 52.5 °C, which was in agreement with the theoretical calculations. The theoretical calculations were conducted on the basis of Mie theory under conditions identical to those used in the experiment. The best photothermal conversion efficiency was obtained using 100 nm TiN NPs prepared by milling at a high rotational speed (600 rpm) for a short time (0.5 h). In addition, experimental and theoretical analyses confirmed that an increasingly amorphous TiN structure impeded the photoheating of the dispersive TiN NP solution. The results of this research have potential implications for indoor environmental heating systems, including heating a room with TiN-embedded walls or floors or distilling water using only visible-light energy.